Steve Flint

Bacterial cell attachment, the beginning of a biofilm

The ability of bacteria to attach to surfaces and develop into a biofilm has been of considerable interest to many groups in numerous industries, including the medical and food industry. However, little is understood in the critical initial step seen in all biofilm development, the initial bacterial cell attachment to a surface. This initial attachment is critical for the formation of a bacterial biofilm, as all other cells within a biofilm structure rely on the interaction between surface and bacterial cell for their survival. This review examines what are believed to be some of the most important aspects involved in bacterial attachment to a surface.

Properties of the stainless steel substrate, influencing the adhesion of thermo-resistant streptococci

Abstract The quality of products produced by dairy manufacturing plant is threatened when bacteria attached to and growing (biofilm formation) on stainless steel are released into the product stream. The adhesion of bacteria to the surface is the first stage in this process and enables subsequent proliferation and release. In the present trial, thermo-resistant streptococci were found to adhere preferentially to stainless steel and zinc substrates compared with other metal and glass substrates and more bacteria adhered to 316L than to 304L grade stainless steel. The adhesion of thermo-resistant streptococci to samples of 304 stainless steel with a range of surface roughness values ( R a 0.5–3.3 μm) or with typical flaws was found to be largely independent of the substrate topography although bacterial entrapment may occur at 0.9 μm.. The rate of adhesion of thermo-resistant streptococci was enhanced in the presence of a hydrophilic substrate, negative electrostatic forces and/or the presence of an oxide coat.

Biofilms in dairy manufacturing plant‐description, current concerns and methods of control

Biofilms on the surfaces of dairy manufacturing plant threaten the quality and safety of dairy products. Biofilms on dairy processing lines are characterised by rapid development ( 106 bacteria ml‐1 and this affects the quality of products manufactured from this milk. Biofilm control currently relies on the effectiveness of clean‐in‐place systems. A shortage of information on the development and control of biofilms in dairy manufacturing plant means that to reduce biofilm problems, increasing the frequency of cleaning is currently the only option for dairy manufacturers.

Control of biogenic amines in food: existing and emerging approaches

Biogenic amines have been reported in a variety of foods, such as fish, meat, cheese, vegetables, and wines. They are described as low molecular weight organic bases with aliphatic, aromatic, and heterocyclic structures. The most common biogenic amines found in foods are histamine, tyramine, cadaverine, 2-phenylethylamine, spermine, spermidine, putrescine, tryptamine, and agmatine. In addition octopamine and dopamine have been found in meat and meat products and fish. The formation of biogenic amines in food by the microbial decarboxylation of amino acids can result in consumers suffering allergic reactions, characterized by difficulty in breathing, itching, rash, vomiting, fever, and hypertension. Traditionally, biogenic amine formation in food has been prevented, primarily by limiting microbial growth through chilling and freezing. However, for many fishing based subsistence populations, such measures are not practical. Therefore, secondary control measures to prevent biogenic amine formation in foods or to reduce their levels once formed need to be considered as alternatives. Such approaches to limit microbial growth may include hydrostatic pressures, irradiation, controlled atmosphere packaging, or the use of food additives. Histamine may potentially be degraded by the use of bacterial amine oxidase or amine-negative bacteria. Only some will be cost-effective and practical for use in subsistence populations.

Thermophilic bacilli and their importance in dairy processing.

The thermophilic bacilli, such as Anoxybacillus flavithermus and Geobacillus spp., are an important group of contaminants in the dairy industry. Although these bacilli are generally not pathogenic, their presence in dairy products is an indicator of poor hygiene and high numbers are unacceptable to customers. In addition, their growth may result in milk product defects caused by the production of acids or enzymes, potentially leading to off-flavours. Dairy thermophiles are usually selected for by the conditions during dairy manufacture. These bacteria are able to grow in sections of dairy manufacturing plants where temperatures reach 40-65°C. Furthermore, because they are spore formers, they are difficult to eliminate. In addition, they exhibit a wide temperature growth range, exhibit a fast growth rate (generation time of approximately 15-20 min) and tend to readily form biofilms. Many strategies have been tested to remove, prevent and/or delay the formation of thermophilic bacilli biofilms in dairy manufacture, but with limited success. This is, in part, because little is known about the structure and composition of thermophilic bacilli biofilms in general and, more specifically, in milk processing environments. Therefore, new cleaning regimes often do not target the problem optimally. A greater understanding of the structure of thermophilic biofilms within the context of the milk processing environment and their link with spore formation is needed to develop better control measures. This review discusses the characteristics and food spoilage potential, enumeration and identification methods for the thermophilic bacilli, as well as their importance to dairy manufacture, with an emphasis on biofilm development and spore formation.

Factors influencing attachment of thermophilic bacilli to stainless steel.

S.G. PARKAR, S.H. FLINT, J.S. PALMER AND J.D. BROOKS. 2001.

Enterocins in food preservation.

The Enterococcus genus, a member of the Lactic Acid Bacteria (LAB) is found in various environments, but more particularly in the intestines of humans and other animals. Although sometimes associated with pathogenicity these bacteria have many benefits. They have been found in traditional artisanal fermented products, are used as probiotic cultures and nowadays extensively studied for the production of bacteriocins--the enterocins. Many of these enterocins have been found to be active against Listeria monocytogenes, and a few have also been reported to be active even against Gram negative bacteria, an unusual property for the bacteriocins produced by LAB. These properties have resulted in many studies describing the use of enterocins as preservatives in foods of animal and vegetable origin. This review covers the most recent information on the use of enterocins as food preservatives, either produced in-situ by the addition of enterocin producing strains or as external preservatives in the form of purified or semi-purified extracts, to prevent the growth of spoilage and pathogenic microorganisms.

The influence of cell surface properties of thermophilic streptococci on attachment to stainless steel

The quality of milk products is threatened by the formation of biofilms of thermophilicstreptococci on the internal surfaces of plate heat exchangers used in milk processing. Althoughattachment to stainless steel surfaces is one of the first stages in the development of a biofilm, themechanisms involved in attachment have not been reported. The cell surface properties of 12strains of thermophilic streptococci were examined to determine their importance in attachment tostainless steel surfaces. Hydrophobicity, extracellular polysaccharide production and cell surfacecharge varied between the different strains but could not be related to numbers attaching. Treatingthe cells with sodium metaperiodate, lysozyme or trichloroacetic acid to disrupt cell surfacepolysaccharide had no effect on attachment. Treatment with trypsin or sodium dodecyl sulphate toremove cell surface proteins resulted in a 100‐fold reduction in the number of bacteria attaching.This result suggests that the surface proteins of the thermophilic streptococci are important intheir attachment to stainless steel.

The growth of Bacillus stearothermophilus on stainless steel

S. FLINT, J. PALMER, K. BLOEMEN, J. BROOKS AND R. CRAWFORD. 2001.

Evaluation of the effect of cleaning regimes on biofilms of thermophilic bacilli on stainless steel.

Aims:  To determine the mechanism for both the removal and inactivation of 18‐h biofilms of a thermophilic Bacillus species that optimally grows at 55°C on stainless steel.